To provide high-molecular compounds with high function, a variety of attempts have been made to date. As a method for providing a high-molecular compound with a high refractive index, for example, it has been practiced to introduce aromatic rings, halogen atoms or sulfur atoms. In particular, high-molecular episulfide compounds with sulfur atoms and high-molecular thiourethane compounds introduced therein have been put into practical use as spectacle lenses of high refractive index.
With a polymer alone, however, it is difficult to design a material of a refractive index higher than 1.7. A method making use of an inorganic metal oxide is, therefore, known as a most promising method for achieving a still higher refractive index.
Methods reported include, for example, a method that achieves an increase in refractive index by using a hybrid material formed by mixing a siloxane polymer with a microparticle-dispersed material in which zirconia, titania or the like is dispersed (Patent Document 1).
Also reported is a method that introduces fused ring skeletons of high refractive index in parts of a siloxane polymer (Patent Document 2).
Numerous attempts have also been made to impart heat resistance to high-molecular compounds. Specifically, it is well known that the heat resistance of a high-molecular compound can be improved by introducing aromatic rings. For example, a polyarylene copolymer with substituted arylene repeating units contained in the backbone thereof has been reported (Patent Document 3). This high-molecular compound is expected to find utility primarily as heat-resistant plastics.
On the other hand, melamine resins are well-known as triazine-based resins. However, they are far lower in decomposition temperature compared with heat-resistant materials such as graphite.
As heat-resistant organic materials formed of carbon and nitrogen, aromatic polyimides and aromatic polyamides have been primarily used to date. However, these materials are not very high in heat-resistant temperature as they have a linear structure.
As nitrogen-containing high-molecular materials having heat resistance, triazine-based fused materials have also been reported (Patent Document 4).
In the meantime, a demand has arisen in recent years for high-functionality, high-molecular materials upon development of electronic devices such as liquid crystal displays, organic electroluminescence (EL) displays, optical semiconductor (LED) devices, solid-state imaging devices, organic thin-film solar cells, dye-sensitized solar cells, and organic thin-film transistors (TFT).
Specific properties to be required include, for example, 1) heat resistance, 2) transparency, 3) high refractive index, 4) high solubility, and 5) lower volume shrinkage rate.
Nonetheless, the above-mentioned spectacle lens materials of high refractive index are generally low in heat resistance, and need to be produced in a temperature range of 200° C. and lower. They are, hence, not suited for processing such as baking at 300° C. under the atmosphere.
Further, high-molecular compounds with aromatic rings or triazine rings introduced therein are generally insufficient in the solubility in solvents, and therefore, are insoluble in resist solvents as safety solvents. On the other hand, materials that exhibit high solubility are generally low in transparency.
On the other hand, materials making use of an inorganic metal oxide can be hardly provided with improved transparency while retaining high refractive index, because refractive index and transparency are in a trade-off correlation.
These materials contain microparticles of different properties, and therefore, involve a problem in that, when subjected to dry processing such as etching or ashing, the etch rate may become unstable, thereby making it difficult to obtain a film of uniform thickness, and upon fabrication of a device, the process margin may become narrow.
Now, highly branched polymers can be roughly divided into hyperbranched polymers and dendrimers.
The term “hyperbranched polymer” means a highly branched polymer having an irregular branched structure obtained by polymerizing, for example, an ABx-type polyfunctional monomer in which A and B are functional groups reactable to each other and the number X of B is 2 or greater.
On the other hand, the term “dendrimer” means a highly branched polymer having a regular branched structure. Hyperbranched polymers are characterized in that compared with dendrimers, they can be easily synthesized and can be readily synthesized in high-molecular forms.
There is an exemplary report that hyperbranched polymers with triazine rings contained therein were synthesized for use as flame retardants (Non-Patent Document 1).